<%@ page contentType="image/jpeg" import="java.util.*,java.awt.*,java.io.*,java.awt.image.*,javax.imageio.*" pageEncoding="utf-8"%>  
<%!  
Color getRandColor(int fc,int bc){//给定范围获得随机颜色  
Random random = new Random();  
if(fc>255) fc=255;  
if(bc>255) bc=255;  
int r=fc+random.nextInt(bc-fc);  
int g=fc+random.nextInt(bc-fc);  
int b=fc+random.nextInt(bc-fc);  
return new Color(r,g,b);  
}  
%>  
<%  
//设置页面不缓存  
response.setHeader("Pragma","No-cache");  
response.setHeader("Cache-Control","no-cache");  
response.setDateHeader("Expires", 0);  
  
// 在内存中创建图象  
int width=60, height=20;  
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);  
  
// 获取图形上下文  
Graphics g = image.getGraphics();  
  
//生成随机类  
Random random = new Random();  
  
// 设定背景色  
g.setColor(getRandColor(200,250));  
g.fillRect(0, 0, width, height);  
  
//设定字体  
g.setFont(new Font("Times New Roman",Font.PLAIN,18));  
  
//画边框  
//g.setColor(new Color());  
//g.drawRect(0,0,width-1,height-1);  
  
// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到  
g.setColor(getRandColor(160,200));  
for (int i=0;i<155;i++)  
{  
int x = random.nextInt(width);  
int y = random.nextInt(height);  
int xl = random.nextInt(12);  
int yl = random.nextInt(12);  
g.drawLine(x,y,x+xl,y+yl);  
}  
  
// 取随机产生的认证码(4位数字)  
String sRand="";  
for (int i=0;i<4;i++){  
String rand=String.valueOf(random.nextInt(10));  
sRand+=rand;  
// 将认证码显示到图象中  
g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));// 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成  
g.drawString(rand,13*i+6,16);  
}  
  
// 将认证码存入SESSION  
session.setAttribute("checkcode",sRand);  
  
// 图象生效  
g.dispose();  
OutputStream output=response.getOutputStream();  
  
// 输出图象到页面  
ImageIO.write(image, "JPEG", response.getOutputStream());  
output.flush();  
out.clear();  
out = pageContext.pushBody();  
  
%> 